Interpretive Summary: New biotechniques, such as genetic engineering and selection of mutants, often require growing plant tissues as cell masses in artificial growth medium. By changing the medium, plants can be regenerated from these tissue cultures. Many factors can affect the number of plants regenerated from tissue cultures, including the growth environment of the donor plants that are used to start these cultures. Growing these donor plants under controlled conditions in a growth chamber results in a consistent number of plants regenerated from cultures, but space in these chambers often is limited. The conditions in a greenhouse are more variable, so this study was designed to identify greenhouse planting times that give the greatest number of regenerated plants, and to compare the results to those from plants grown in a growth chamber. Cultures from plants sown in the greenhouse in December regenerated significantly fewer green plants than cultures from plants sown at other times of the year. The reduced regeneration in December appears to be caused by reduced light levels during the winter months. Temperature differences at various times of the year were small and had little effect on the number of plants regenerated from cultures. The results show that sufficient plant regeneration from cultures of plants grown in the greenhouse can be obtained when natural light levels are high and temperatures are moderate. Plants grown under these conditions can be used to establish tissue cultures for use in genetic engineering and mutant selection.

Technical Abstract:
High levels of green plant regeneration are necessary for efficient barley (Hordeum vulgare L.) transformation. Experiments to optimize regeneration of calli derived from immature embryos have examined the effects of genotype and media components, but research on the effects of donor plant growth environment are lacking. Defined growth conditions in growth chambers are known to give consistent regeneration rates, but space often is limited. The objective of this project was to evaluate regeneration from barley tissue cultures of Golden Promise and Morex grown under greenhouse conditions, planted at four different times, to determine optimal greenhouse planting times; results were compared to cultures from plants grown in the growth chamber at the same four planting dates. Genotype, growth environment, and planting date had significant effects on green plant regeneration. Cultures of embryos from plants sown in the greenhouse in December resulted in significantly fewer green regenerants per plate. Regeneration was more dependent on the average solar radiation than on temperature. The best greenhouse regeneration rates for Morex were not significantly different than regeneration from growth chamber-grown donor plants. Green plant regeneration was higher and less variable from growth chamber-grown donor plants. Sufficient regeneration from greenhouse-grown donor plants can be reached when natural light levels are high and temperatures are moderate.